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G Pepeu

Publications and source records attributed to G Pepeu.

At least 19 recordsLinked to original sources
PubMed2005

Inhibition of acetylcholine-induced activation of extracellular regulated protein kinase prevents the encoding of an inhibitory avoidance response in the rat.

It has been demonstrated that the forebrain cholinergic system and the extracellular regulated kinase signal transduction pathway are involved in the mechanisms of learning, encoding, and storage of information. We investigated the involvement of the cholinergic and glutamatergic systems projecting to the medial prefrontal cortex and ventral hippocampus and of the extracellular regulated kinase signal transduction pathway in the acquisition and recall of the step-down inhibitory avoidance response in the rat, a relatively simple behavioral test acquired in a one-trial session. To this aim we studied by microdialysis the release of acetylcholine and glutamate, and by immunohistochemistry the activation of extracellular regulated kinase during acquisition, encoding and recall of the behavior. Cholinergic, but not glutamatergic, neurons projecting to the medial prefrontal cortex and ventral hippocampus were activated during acquisition of the task, as shown by increase in cortical and hippocampal acetylcholine release. Released acetylcholine in turn activated extracellular regulated kinase in neurons located in the target structures, since the muscarinic receptor antagonist scopolamine blocked extracellular regulated kinase activation. Both increased acetylcholine release and extracellular regulated kinase activation were necessary for memory formation, as administration of scopolamine and of extracellular regulated kinase inhibitors was followed by blockade of extracellular regulated kinase activation and amnesia. Our data indicate that a critical function of the learning-associated increase in acetylcholine release is to promote the activation of the extracellular regulated kinase signal transduction pathway and help understanding the role of these systems in the encoding of an inhibitory avoidance memory.

Acetylcholine↗
PubMed2005

Proteomic identification of proteins specifically oxidized by intracerebral injection of amyloid beta-peptide (1-42) into rat brain: implications for Alzheimer's disease.

Protein oxidation has been shown to result in loss of protein function. There is increasing evidence that protein oxidation plays a role in the pathogenesis of Alzheimer's disease (AD). Amyloid beta-peptide (1-42) [Abeta(1-42)] has been implicated as a mediator of oxidative stress in AD. Additionally, Abeta(1-42) has been shown to induce cholinergic dysfunction when injected into rat brain, a finding consistent with cholinergic deficits documented in AD. In this study, we used proteomic techniques to examine the regional in vivo protein oxidation induced by Abeta(1-42) injected into the nucleus basalis magnocellularis (NBM) of rat brain compared with saline-injected control at 7 days post-injection. In the cortex, we identified glutamine synthetase and tubulin beta chain 15/alpha, while, in the NBM, we identified 14-3-3 zeta and chaperonin 60 (HSP60) as significantly oxidized. Extensive oxidation was detected in the hippocampus where we identified 14-3-3 zeta, beta-synuclein, pyruvate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, and phosphoglycerate mutase 1. The results of this study suggest that a single injection of Abeta(1-42) into NBM can have profound effects elsewhere in the brain. The results further suggest that Abeta(1-42)-induced oxidative stress in rat brain mirrors some of those proteins oxidized in AD brain and leads to oxidized proteins, which when inserted into their respective biochemical pathways yields insight into brain dysfunction that can lead to neurodegeneration in AD.

Amyloid beta-Peptides↗
PubMed2003

The selective cyclooxygenase-2 inhibitor rofecoxib suppresses brain inflammation and protects cholinergic neurons from excitotoxic degeneration in vivo.

Brain inflammatory processes underlie the pathogenesis of Alzheimer's disease, and non-steroidal anti-inflammatory drugs have a protective effect in the disease. The aim of this work was to study in vivo whether attenuation of brain inflammatory response to excitotoxic insult by the selective cyclooxygenase-2 inhibitor, rofecoxib, may prevent neurodegeneration, as a contribution to a better understanding of the role inflammation plays in the pathology of Alzheimer's disease. We investigated, by immunohistochemical methods, glia reaction, the activation of p38 mitogen-activated protein kinase (p38MAPK) pathway with an antibody selective for the phosphorylated form of the enzyme and the number of choline acetyltransferase-positive neurons and, by in vivo microdialysis, cortical extracellular levels of acetylcholine following the injection of quisqualic acid into the right nucleus basalis of adult rats. Seven days after injection, a marked reduction in the number of choline acetyltransferase-positive neurons was found, along with an intense glia reaction, selective activation of p38MAPK at the injection site and a significant decrease in the extracellular levels of acetylcholine in the cortex ipsilateral to the injection site. The loss of cholinergic neurons persisted for at least up to 28 days. Rofecoxib (3 mg/kg/day, starting 1 h prior to injection of quisqualic acid) treatment for 7 days significantly attenuated glia activation and prevented the loss of choline acetyltransferase-positive cells and a decrease in cortical acetylcholine release. The prevention of cholinergic cell loss by rofecoxib occurred concomitantly with the inhibition of p38MAPK phosphorylation. Our findings suggest an important role of brain inflammatory reaction in cholinergic degeneration and demonstrate a neuroprotective effect of rofecoxib, presumably mediated through the inhibition of p38MAPK phosphorylation.

Alzheimer Disease↗
PubMed2003

Investigation on acetylcholine, aspartate, glutamate and GABA extracellular levels from ventral hippocampus during repeated exploratory activity in the rat.

The extracellular levels of aspartate, glutamate, gamma-aminobutyric acid (GABA), and acetylcholine (ACh) were investigated by microdialysis, coupled with HPLC, in the ventral hippocampus of rats during two 30-min exploration periods. Motor activity was monitored. During exploration I, an increase in motor activity associated with a 315% increase in aspartate, 181% in glutamate, and 264% in ACh levels, occurred during the first 10 min. The increase in GABA level reached a maximum of 257% during the second 10 min. The neurotransmitter levels returned to basal values within 40 min. During exploration II, 1 h later, a smaller increase in neurotransmitter levels and motor activity was observed. In both explorations, the increase in neurotransmitter levels was completely abolished by 1 and 3 microM TTX. A statistically significant relationship was found between neurotransmitter extracellular levels and motor activity, for aspartate and glutamate in exploration I, and for ACh in exploration I and II. In conclusion, exploratory activity is associated with or depends on the activation of neuronal systems in the ventral hippocampus releasing aspartate, glutamate, GABA, and ACh. The activation is dampened by habituation.

Acetylcholine↗
PubMed2002

Effect of subchronic administration of metrifonate, rivastigmine and donepezil on brain acetylcholine in aged F344 rats.

The changes in extracellular acetylcholine levels were investigated by microdialysis in the cortex and hippocampus of aging rats after administration of metrifonate (80 mg/kg), rivastigmine (0.75 mg/kg), donepezil (1.5 mg/kg) or vehicle for 21 days (twice daily p.o.). Eighteen h after the last administration, cholinesterase inhibition was 85, 52 and 39% after metrifonate, rivastigmine and donepezil, respectively, and was accompanied by 988, 590 and 75% increase in cortical acetylcholine level. In the hippocampus, metrifonate and rivastigmine brought about a 169 and 108% increase in acetylcholine levels. A challenge dose of metrifonate, rivastigmine and donepezil was followed by a further increase in cortical and hippocampal acetylcholine levels. The retrograde perfusion of the M(2)-M(4) receptor antagonist AFDX-384 (10 microM) induced a 500 and 300% increase in cortical and hippocampal acetylcholine release, in control and rivastigmine-treated rats, respectively, no increase in metrifonate-treated rats, and a 210% increase in donepezil-treated rats. In conclusion, chronic treatment of aging rats with metrifonate, rivastigmine and donepezil induces a long-lasting increase in acetylcholine levels, and reveals marked differences between the three drugs.

Acetylcholine↗
PubMed2002

Rivastigmine antagonizes deficits in prepulse inhibition induced by selective immunolesioning of cholinergic neurons in nucleus basalis magnocellularis.

Impairments of cortical cholinergic inputs from the nucleus basalis magnocellularis fundamentally alter information processing and attentional function, thereby advancing the severity of psychopathology in major neuropsychiatric disorders. It was previously shown in adult rats that bilateral 192 IgG saporin-induced selective immunolesioning of the cholinergic neurons in the nucleus basalis produces pronounced and long-lasting deficits in sensorimotor gating measured by prepulse inhibition of the startle reflex. This behavioral paradigm is considered a valid model of sensorimotor gating deficits in the psychotic spectrum and efforts to analyze the significance of the cholinergic basal forebrain in this context are of great interest. In the present study the predictive value of the selective cholinergic immunolesioning model was tested by examining the ability of the cholinesterase inhibitor rivastigmine to restore prepulse inhibition in immunolesioned rats. We report here a pronounced restoring effect of acute (0.75 or 1.5 mg/kg s.c.) as well as repeated (0.75 mg/kg s.c. b.i.d., for 10 days) treatment with rivastigmine in this model of disrupted prepulse inhibition. Intra-nucleus basalis magnocellularis infusions of 192 IgG saporin resulted in extensive loss of basal-cortical cholinergic neurons as shown by the marked decrease in basal telencephalic choline acetyltransferase immunopositive neurons and cortical choline acetyltransferase activity. In this condition, rivastigmine was found to significantly increase cortical acetylcholine extracellular levels in lesioned animals measured by in vivo microdialysis. Taken together, our results strengthen the proposal that the nucleus basalis represents a critical station of the startle gating circuitry. In addition, our findings strongly indicate that even after dramatic decrease of cholinergic neurons, inhibition of acetylcholinesterase restores the cholinergic synaptic function to a point approaching normalization of experimentally induced psychopathology.

Acetylcholine↗
PubMed2001

Changes in presynaptic proteins, SNAP-25 and synaptophysin, in the hippocampal CA1 area in ischemic gerbils.

A general consensus exists that the presynaptic terminals in the hippocampal CA1 area are resistant to ischemic stress in spite of the loss of their target cells (CA1 pyramidal neurons). We have verified this by immunostaining and Western immunoblotting using the antibodies for presynaptic proteins, synaptosomal-associated protein of 25 kDa (SNAP-25) and synaptophysin in gerbils after bilateral carotid artery ligature. In the immunohistochemical analysis, decreases in SNAP-25 and synaptophysin immunoreactivities in the strata radiatum and oriens, especially around the apical dendrite of CA1 neurons, and disappearance of SNAP-25 immunoreactivity in the alveus were observed on day 2 after ischemia. On days 7 and 14, SNAP-25-positive granular materials were expressed in the CA1 area, and intense synaptophysin immunoreactivity around surviving CA1 neurons was observed. Western immunoblot analysis revealed significant decreases of SNAP-25 and synaptophysin (about 60% of control levels) on day 2, and then increase of their proteins (130--140% of control levels) on day 14. These results indicate that presynaptic degeneration occurs in the hippocampal CA1 area after ischemia, and it precedes the delayed neuronal death of CA1 neurons. The presynaptic terminal damage may be responsible for some pathological changes in ischemic brains.

Animals↗
PubMed2001

NO synthesis inhibition decreases cortical ACh release and impairs retention of a conditioned response.

We investigated in rats the effect N(G)-nitro-L-arginine methyl ester (L-NAME) on retention of a passive avoidance response, and cortical ACh release monitored using the microdialysis technique. Post-training administration of L-NAME impaired 24 h retention of a passive avoidance and decreased cortical ACh release. Both effects of L-NAME were reversed by L-Arg. These results suggest that nitric oxide is involved in retention of the passive avoidance response through the modulation of the forebrain cholinergic system.

Acetylcholine↗
PubMed2001

Overview and perspective on the therapy of Alzheimer's disease from a preclinical viewpoint.

1. Drugs effective in Alzheimer's disease (AD) should have several aims: to improve the cognitive impairment, control the behavioural and neurological symptoms, delay the progression of the disease, and prevent the onset. In order to attain these targets, cell and animal models are needed on which to test pathogenetic hypothesis and demonstrate the potential effectiveness of new drugs. This overview examines the results obtained in animal models. They are the link between the molecular and biochemical studies on the disease and the reality of human pathology. 2. The development of animal models reproducing the complexity of AD pathogenetic mechanisms and clinical symptoms still represents a challenge for the preclinical investigators. Moreover, the succession of different animal models well documents the progressive widening of our knowledge of the disease with the identification of new therapeutic targets. 3. The main animal models are listed, and their contribution to the understanding of the pathogenic mechanisms and development of the drugs presently used in AD therapy is described. Moreover, their role in the study of future drugs is analysed 4. Preclinical studies on cholinesterases and animal models mimicking the cholinergic hypofunction occurring in AD have been instrumental in developing cholinesterase inhibitors, which are the only recognised drugs for the symptomatic treatment of AD. 5. Artificially created beta-amyloid (A beta) deposits in normal rats, and transgenic mice overexpressing amyloid precursor protein (APP) are the models on which the future treatment are tested. They are aimed to prevent formation of A beta deposits or its transformation in neuritic plaques. 6. Models of brain inflammation, aging animals, and models of brain glucose and energy metabolism impairment make it possible to identify and assess the activity of anti-inflammatory agents, antioxidants, ampakines and other potentially active agents. 7. It is concluded that the present level of information on AD could never have been reached without preclinical studies, and the development of new drugs will always require extensive preclinical investigations.

Aging↗
PubMed2001

Effects of novelty and habituation on acetylcholine, GABA, and glutamate release from the frontal cortex and hippocampus of freely moving rats.

The involvement of the forebrain cholinergic system in arousal, learning and memory has been well established. Other neurotransmitters such as GABA and glutamate may be involved in the mechanisms of memory by modulating the forebrain cholinergic pathways. We studied the activity of cortical and hippocampal cholinergic, GABAergic and glutamatergic systems during novelty and habituation in the rat using microdialysis. After establishing basal release of the neurotransmitters, the animals were transferred to a novel environment and allowed to explore it twice consecutively for 30 min (60 min apart; exploration I and II). The motor activity was monitored. Samples were collected throughout the experiment and the release of acetylcholine (ACh), GABA and glutamate was measured. During the two consecutive explorations of the arena, cortical and hippocampal, ACh release showed a significant tetrodotoxin-dependent increase which was higher during exploration I than II. The effect was more pronounced and longer-lasting in the hippocampus than in the cortex. Cortical GABA release increased significantly only during exploration II, while hippocampal GABA release did not increase during either exploration. Motor activity was higher during the first 10 min of exploration I and II and then gradually decreased during the further 20 min. Both cortical and hippocampal ACh release were positively correlated with motor activity during exploration II, but not during I. During exploration II, cortical GABA release was inversely correlated, while hippocampal GABA release was positively correlated to motor activity. No change in cortical and hippocampal glutamate release was observed. In summary, ACh released by the animal placed in a novel environment seems to have two components, one related to motor activity and one related to attention, anxiety and fear. This second component disappears in the familiar environment, where ACh release is directly related to motor activity. The negative relationship between cortical GABA levels and motor activity may indicate that cortical GABAergic activity is involved in habituation.

Acetylcholine↗
PubMed2001

Selective immunolesioning of cholinergic neurons in nucleus basalis magnocellularis impairs prepulse inhibition of acoustic startle.

Information processing and attentional abnormalities are prominent in neuropsychiatric disorders. Since the cholinergic neurons located in the nucleus basalis magnocellularis have been shown to be involved in attentional performance and information processing, recent efforts to analyze the significance of the basal forebrain in the context of schizophrenia have focused on this nucleus and its projections to the cerebral cortex. We report here that bilateral selective immunolesioning of the cholinergic neurons in the nucleus basalis magnocellularis is followed by significant deficits in sensorimotor gating measured by prepulse inhibition of the startle reflex in adult rats. This behavioral approach is used in both humans and rodents and has been proposed as a valuable model contributing to the understanding of the neurobiological substrates of schizophrenia. The disruption of prepulse inhibition persisted over repeated testing. The selective lesions were induced by bilateral intraparenchymal infusions of 192 IgG saporin at a concentration having minimal diffusion into adjacent nuclei of the basal forebrain. The infusions were followed by extensive loss of choline acetyltransferase-immunopositive neurons. Our results show that the cholinergic neurons of the nucleus basalis magnocellularis represent a critical station of the startle gating circuitry and suggest that dysfunction of these neurons may result in impaired sensorimotor gating characteristic of schizophrenia.

Acetylcholine↗
PubMed2001

NO-flurbiprofen attenuates excitotoxin-induced brain inflammation, and releases nitric oxide in the brain.

Brain inflammation underlies the pathogenesis of Alzheimer's disease (AD) and nonsteroidal anti-inflammatory drug therapy may delay the onset of AD. We investigated, in vivo, the effects of NO-flurbiprofen on brain inflammation in rats injected with quisqualic acid into the nucleus basalis and on the release of nitric oxide from the drug in naive rat brains. We showed that the excitotoxin-induced microglia reaction, the expression of inducible nitric oxide synthase-positive cells and the production of interleukin-1beta and prostaglandin-E2 in the injected area were attenuated by the NO-flurbiprofen (15 mg/kg, p.o.) treatment. An oral administration of NO-flurbiprofen (25, 50 and 100 mg/kg) to naive rats was followed by significant increases in cortical nitrite levels. This drug may have important therapeutic implications for the treatment of AD.

Animals↗
PubMed2000

NGF treatment potentiates c-fos expression in the rat nucleus basalis upon excitotoxic lesion with quisqualic acid.

The induction of the c-fos gene in the rat brain by NGF was studied in a model of acute cholinergic hypofunction, i.e., the lesion of the nucleus basalis magnocellularis (NBM) with quisqualic acid. Choline acetyltransferase and Fos immunoreactivity (IR) in the NBM were analyzed at different times after the excitotoxic lesion. NGF treatment induced a potentiation of Fos expression 4 and 24 h after lesion. The possibility is discussed that c-fos induction is one of the early mechanisms of the neuroprotective action of NGF.

Animals↗
PubMed2000

Brain inflammatory reaction in an animal model of neuronal degeneration and its modulation by an anti-inflammatory drug: implication in Alzheimer's disease.

Brain inflammatory processes underlie the pathogenesis of Alzheimer's disease, and nonsteroidal anti-inflammatory drugs have a protective effect in the disease. The aim of this study was to characterize in vivo in the rat brain the inflammatory reaction in response to excitotoxic insult and to investigate the efficacy of nimesulide treatment. Quisqualic acid was injected into the right nucleus basalis of rats. The excitotoxin induced cholinergic degeneration, an intense glial reaction and the production of inflammatory mediators. Three hours after injection, a five-fold elevation in the concentration of interleukin-1beta in the injected area was observed. This elevation was reduced by 50% by nimesulide (10 mg/kg, i.m.) pretreatment. Electron microscope examination and immunocytochemical staining revealed an intense activation of microglia and astrocytes at both 24 h and 7 days after injection. Cyclooxygenase-2-immunoreactivity was induced in the blood vessels of the injected hemisphere in perivascular microglial and endothelial cells 24 h after injection. Seven days postinjection, a cyclooxygenase-2-positive signal was induced in the parenchymal microglia and large amounts of prostaglandin-E2 were measured in the injected area. Twenty-four hours and 7 days after injection, many inducible nitric oxide synthase-positive cells and a high level of nitrite were detected at the injection site. Seven days of nimesulide (10 mg/kg/day, i.m.) treatment strongly attenuated the microglial reaction, reduced the number of inducible nitric oxide synthase-positive cells and completely abolished the increase in prostaglandin-E2 formation. These data provide valuable support in vivo for the potential efficacy of cyclooxygenase-2 inhibitors in Alzheimer's disease therapy.

Acetylcholine↗
PubMed1999

Effect of adenosine A2A receptor stimulation on GABA release from the striatum of young and aged rats in vivo.

The effect of the adenosine A2A receptor agonist CGS 21680 on GABA release from the striatum was investigated in vivo in young and old rats by microdialysis experiments. CGS 21680 at 10 microM significantly increased GABA spontaneous outflow in young but not in old rats. Conversely, CGS 21680 significantly increased potassium-evoked GABA release in old but not in young rats. The stimulating effect of CGS 21680 on spontaneous GABA release may be both secondary to an increased outflow of excitatory amino acids and to the removal, brought about by A2A receptor stimulation, of the inhibitory influence exerted by dopamine through D2 receptors on GABA-enkephalinergic neurones. The stimulating effect of CGS 21680 on potassium-evoked GABA release in old rats may be ascribed to an age-dependent imbalance in favour of adenosine vs. dopamine, recently described in the striatum of old rats.

Adenosine↗
PubMed1999

Trazodone increases extracellular serotonin levels in the frontal cortex of rats.

The effects of the antidepressant drug, trazodone, on the extracellular 5-hydroxytryptamine (5-HT) levels in the frontal cortex of freely moving rats was investigated using microdialysis coupled to a high performance liquid chromatography (HPLC) detection method. Systemic administration of 1.25 and 2.5 mg/kg s.c. of trazodone was followed by a rise in the 5-HT level which reached a 5-fold peak over the basal level 5 h after injection, and a 3-fold peak after 1 h. Higher doses had no effect. The increase was prevented by pretreatment with fluoxetine (10 mg/kg s.c.), a 5-HT uptake inhibitor. Direct administration of trazodone (0.03, 0.1, 1, 2 microg/microl), by reverse dialysis into the frontal cortex, elicited a dose-dependent large increase in 5-HT levels. The increase was not prevented by systemic fluoxetine administration but was reduced by local perfusion of ketanserin (0.1 microg/microl) a 5-HT(2A/C) receptor antagonist. Trazodone s.c. administration for 7 days did not increase 5-HT basal levels but enhanced the effects of challenge doses of 2.5 and 5 mg/kg s.c. The present work demonstrated that trazodone increases the 5-HT extracellular level through a double mechanism which involves the 5-HT transporter and 5-HT(2A/C) receptors. This increase may trigger the chain of events which lead to the therapeutic effects, similar to the case of many other antidepressant drugs.

Animals↗
PubMed1999

Beta(1-40) amyloid peptide injection into the nucleus basalis of rats induces microglia reaction and enhances cortical gamma-aminobutyric acid release in vivo.

The nucleus basalis of adult rats was injected with beta(1-40) amyloid peptide. A marked increase in basal and K(+)-evoked GABA release in the ipsilateral cortex and a significant decrease in GAD activity in the injected NB were found 30 days after injection. An intense activation of microglial cells that surrounded and infiltrated the deposit was observed. These data demonstrate that a local injection of beta(1-40) peptide into the NB induces glia activation and affects GABAergic neurons.

Amyloid beta-Peptides↗